Art of nullifying inductive disturbances.



W. E. ATHEA RN. v ART OF'NULLIFYING INDUCTIVE DISTURBANGES.

APPLICATION FILED APR. 29. 1908.

' Patented Nov. 23, .1909.

'lliILLIAIVL IE. ATHEARN, OF NEW YORK, N. Y., ASSIGNGR T0 AMERICAN TELEPHGNE AND TELEGBA PH CQMPANY, A CORPORATION OF NEW YORK.

Specification of Letters Patent.

Patented Nov.

Application filed April 29, 1908. Serial No. 429,973.

To all whom it may concern:

Be it known that 1, WILLIAM E. ATHEARN, residing at New York, borough of Brooklyn, in the county of Kings and State otliew York, have invented certain Improvements in the Art of Nullifying Inductive Disturbances, of which the following is a specificatron.

Circuits for telephonic and telegraphic communication, or other lines over which electrical signals are transmitted under comparatively low potentials, are liable to be subjected to the inductive influence of such alternating current power circuits as are used for the propulsion of heavy railway trains at high speeds. These power systems frequently operate with excessive currents and at a relatively low frequency, twenty-live cycles, and have been found sometimes to setup in adjacent conductors electron'iotive forces often amounting to from one hundred and fifty to three hundred volts and sometimes reachlng eighthundred volts. Under such conditions a' grounded telegraphic circuit, as usually organized, is rendered inoperative, the induced twenty-live cycle current, even if not under much pressure, causing the relay armatures to so vibrate that the Morse signals are rendered unintelligible. Vith metallic circuits, as those of the telephone, no matter how carefully they are transposed, they still may be seriously afliected when the induced electromotive force reaches about two hundred volts, since it then begins to discharge at the lightning arr-esters, and to the listurbaiu:e thus produced is addedthc hazard of lire from i.nsullicient insulation and of painful shocks to subscribers and operators. To

"' prevent these difficulties, it has been pro plural secondary windings of one or more properly designed induction coils, there being one of these secondary windings connected in each signaling conductor, while a primary winding for 'nducing in the secondaries the neutralizing electroniotive forces in a circuit under the saline inductive influence as said signaling comluctors. To attain the best results the resistance of the primary circuit of each induction coil must be low, and therefore the rimary Winding consists ot a conductor. 0 relatively large cross section. To continue this low resist ance throughout the circuit of the primaries.

the conductors making up the remainder of this neutralizing circuit must also he of small resistance, and since, as already pointed out, their exposure must be the that of the lines in which disturbances are to he abated, it has een .to'und convenient to set aside from the latter a sufiicient nuin her to give the requisite conductivity, connee ing' these in multiple to each primary winding and grounding, their extremities outside the affected district to permit a flow of the primary neutralizing current. It will be evident that the lines thus employed are useless'tor the purposes for which they were intended, since. their connection with the single primary winding makes them in effect :1. single conductor and the ground connections carry off the signaling as well the neut alizing currents. There must co11sequently be counted against this system, in

addition to the comparatively small invest ment in induction coils, charges for the neutralizing conductors amounting to at least twenty-five per cent. of the expenditure for those protected. Though gain is made, it is at a heavy cost, and the purpose of the present invention is to minimize this loss in conductors.

With this end in view, my invention consists in a method of utilizing for transmission the primary conductors and ahatinn' therein the cll'cct of the directly induced electroniotiyc forces which develop in the K secondary conductors the neutralizing electromotive forces.

'In the accompanying drawing is illustrated diagrammatically one system by which my method may be carried-out. Here the grounded power conductor Z, for high potential, low frequency alternating current, is shown extending in proximity and substantially parallel to a number oi? conductors L, L", which it is desired to employ for telephonic and telegraphic communication. It may be assumed that the conductors L L are practically equidistaut from. Z. ln the present instance the conductors are arranged in twisted pairs, and aretherefore adapted for metallic telephone circuits, hut they may be also used independently of their application to telephone purposes or simultaneously therewith for grounded telegraph circuits, in the latter case either singly or in pairs by the wellknown composite or simplex'methods. The current traversing the power conductor will induce'in the signaling lines electromot-ive forces, tending to produce the disturbing currents and discharges previously mentioned.

nected' with them in series a single low resistance primary winding t of at least one.

induction coil or transformer T. At points beyond the ends of the'power conductor the line conductors of groupc are connected to ground or other common return at Gr, G through apparatus which will be later considered, since it does not enter into the operation of that portion of the system now being described. Each transformer has a plurality of secondary windings 25 each consisting of a pair of conductors and preferably equaling in number the pairs in the line group b.

The design of the transformer is governed by the following general considerations: The passage of the disturbing current through the conductor Z will induce in each of the signaling conductors L and L substantially equal electromotive forces In the primary group a this electromotive force .will cause a flow of current through the circuit completed by the common return, which, traversing the primary windings t of the transformers, generates an electromotive force in each of the secondary windings The secondarywindings are so related to the primaries and so connected to the conductors L", that the transformer electromotive force of the secondary conductors opposes that directly induced by the power conductor. Then by supplying each second-' ary coil with a greater number of turns than its primary to provide for losses in the primary conductors and in transformation, this secondary electromotive force may bemade practically to nullify the disturbing electromotive force. Complete compensation cannot be obtained by such a transformer, because of differences in wave form and phase between the directly induced and secondary clectromotivc forces in the 'conductors L caused by cl'iaracteristics of the transformer. This effect, however, may be minimized by the use of an efficient transformer and by keeping down the resistance of the primary circuit, the latter condition being obtained by the large primary winding and the multipling with it of a number of the line conductors L The number of transformers used depends upon the length of the groups of lines to be protected and the magnitude of the electromotiyeforce induced,.since each of said transformers 'will carry its proportionate part of the total voltage, and to distribute this among aplurality of transformers increases the factor of safety case of accident. In the present instance two of these are shown, and the primary windings ofthese transformers may be considered to separate the conductors L into three section 7 It will be seen that the above system will render each of the lines or circuits of group a electrically continuous independently of the associated lines in said group and of the windings of the transformers, and to provide for the neutralizing primary current a path to the common return which shall eitclude operating currents.

In the system as illustrated, 1 secure the continuity of each pair of conductors by associating their successive sections independently of the primaries 'of the transformer through repeating coils R having elec-' trically symmetrical sectional windings r, r, and r T The opposite extremities'of the primary t of each transformer T are joined in multiple with the centers of the windings ofall the repeating coils connected to the samepair of line sections, that is, to points at the junctures of the coil sections 1, r, and 7*, "1", by conductors 10 and 11, respectively. Electrical signaling impulses of a pulsatory or alternating character, such as telephone currents, originated, for. example, at a station A, flow in bothsides of the first section in the circuit furnished by a pair of conductors L, passing serially through the coil. windings '1', r and inducing .similar currents in the associated windings r r Transmission will thus continue throughout the circuit to station B each winding '1, r acting as the primary and 1- 1' as the secondary of an induction coil, the relation being re-. versed when transmission occurs in the oppos site direction. The induced primary 'cur-. rent, which is to be used in the production of the compensating secondary currents, traverses each pair of line conductors L in' parallel, inward throughboth sections of the winding 2", 9" of the firsu repeatingcoil, conductor 10, the primary of the first trans power conductor is equal and opposite in both sides of the line pair and in both'sections of the repeating coil windings, itwill. be balanced and without effectupon the op-- erating current,

U furnish a selective ground connection for the neutralizing current I have shown bridged across each line pair beyond the op posits extremities of the disturbing conductor if, a suitable impedance coil 1 with its center united to the ground G' by a conductor 12. To the telephone currents passing in the same direction through their entire length these coils present so high impedance 113 to be practically opaque or exclusive thereto, but for the induced current flowing in opposite directions through the halves, they act differentially and become readily permissiye. In this manner operating currents arecoiiiined to the metallic circuit in which they are originated, while the primary neutralizing current circulates in the conductors L in parallel and through the common ground return.

From What has been stated, it will be seen that l have provided a method whereby the group of conductors L not only performs its function of protecting the companion group L against inductive disturbances, but

which also permits a not greatly affected transmission of signaling currents through the first group. There yet remains to be considered the effect upon the system of the electromotive force which producesthe'primary neutralizing current. If this were equal to the inductively impressed electromotive force it might, under some conditions of circuits and exposurefloe so great as to lead to the disruptive discharges and to cause fires and shocks as has beendescribed. But the transformers, by the self-induction of their primaries will generate a counter electromotive force opposing the impressed elect-romotive force and approaching it in magnitude, the difi'erence being the voltage necessary to send the transformer magnetizing current through the primary circuit. its the transformers are designed to operate eiiiciently and the resistance of the primary circuit is comparatively small, the resultant electromotive force will be too low to be detrimental. The group a of signaling conduotors will therefore be as fully protected against induction as is the group-Z To avoid confusion in the diagram, the primary and secondary windings of the transformers T appear upon separate cores.

in practice, however, to increase the eiiicieucy of transformation, the coils j are superposed uponboth cores. A suitable arrangeinent'has heen found to consistfof a' primary winding-distributed uniformly over opposite cores. hundred and fifty turns of insulated copper tape, having sectional dimensions of seventytwo thousandths of an inchby oneand three' tenths inches and a total resistanceof about four tenths of'an ohm, .Over this the plural secondaries are placed side by side on both cores, eaclrhaving the samenumberof turns It isfurnished by three of pairedwindings as the primary and being of number twenty-insulated copper wireI each of th'csewires presenting a resistance of approximately fiveand seventy five hundredths ohms. V Taps arebrought outfrom the primary winding whereby the number. I

of turns may be reduced by amounts varying up to about-fifteen per cent. of the total to give the desired ratio of transformation. The repeating coils and impedance coils need not be particularly described, as standard apparatus may be employed.

In my application, Serial Number 429,974 filed April 29th, 1908, I have claimed asystem shown and described but not claimed herein.

I claim:

1. The method of arranging for communication, lines employed in inducing neut-alizing electromotive forces in other lines of comuuuiication, which consists in rendering each of the neutralizing lines electrically continuous independently of its associated neutralizing lines, and providing-for the inducing currents a path separate from the neutralizing lines, such path excluding ope crating currents. 2. The method of protecting from indutive disturbances a plurality of signaling conductors, which consists in dividing the conductors into groups, providing in each group one or more signaling circuits, fun nishing from each conductor in one group a path to acommon return, said paths being permissive to induced currents but exclusive to signaling currents, and causing the induced electromotive force in the last-named group to induce in a second group an electromotive force in opposition to that caused by direct induction from the disturbing source.

3. The method of nullifying inductive effects in signaling conductors,'which .consists in providing a path to ground from said conductors permissive to currents resulting from theinduced electromotive force of inducing electromotive forces in other lines of said system to neutralize inductive effects produced in all the lines by some source external thereto, which consists in establishing paths for signaling currents in the neutralizing group of lines, said paths being independent of other similar paths in the same group and each path serving also to conduct induced currents, and separating the induced from the signaling currents over portions of the paths.

5. The method of arranging circuits for the transmission of signals over a group of lines employed in a system for the purpose of inducing electromotive forces in other lines of said system to neutralize inductive effects produced in all the lines by' some source external thereto, which consists in es-. tuhlishing conducting paths in the neutralizin grou of lines, said paths being independent 0 other similar paths in the same group and serving to conduct neutralizing currents resulting from the induced e1 ectromotive forces, generating in the neutralizing group of lines counter electromotive forces approachin in magnitmie the induced electroniotive orces, passing distinct signaling currents through the independent paths, and separating the induced from the signaling currents over portions of the paths.

--'In testimony whereof, I have signed'my name to this specification in the presence of two subscribing Witnesses, this 23rd day of WILLIAM E. ATHEARN. Vitnesses: I

Ronnnr Fos'rER James,

SYLvANUs ll. Conn. 

